1. Field of the Invention
This invention relates to the art of concrete joint forms that are supported on a plurality of metal stakes to provide a key joint forming member between adjacent slab sections of a monolithically poured concrete slab.
2. Description of the Prior Art
The Wilbur U.S. Pat. No. Re. 24,921 describes a concrete slab key-joint forming member that is supported on a plurality of widely-spaced metal stakes which enables slabs of concrete to be poured simultaneously on both sides of the key-joint forming member. One of the problems experienced with these products has been the possibility of the form not gripping the stake rigidly enough to prevent the form from slipping and floating off before or during the pouring of the concrete.
The next patent to Gaetke U.S. Pat. No. 3,288,042 describes a concrete slab key joint forming strip that is supported on a plurality of widely-spaced metal stakes. The top end of each stake is provided with an aperture. There is a special tool provided for crimping the lower edge of a downturned flange into the aperture for locking the form onto the stake and preventing inadvertent removal of the form from the stake. The use of this tool increases the labor cost of installing these forms on these stakes.
The Tone U.S. Pat. No. 3,401,612 is another patent like that of Gaetke, except that the upper end of the stake does not have an aperture, but it has a notch in each of the opposite sides of the stake so that a tool, such as a crescent wrench, may be used to deform the lower edge of the downturned flange until it interlocks with the notch and makes a mechanical connection between the form and the stake. However, the labor costs for making these adjustments are a disadvantage in using the Tone invention.
The Collier U.S. Pat. No. 3,784,313 describes a concrete slab key joint forming strip that is supported on a plurality of widely-spaced metal stakes. This design provides a means for attaching a concrete slab key joint forming strip to a supporting stake without requiring the use of special tools for assembly of the forming strip on the support stake. The upper end of the forming strip had a generally inverted U-shaped cross section with a base portion having a downwardly-extending hook portion extending from one side thereof and terminating in a distal edge in the form of a weak inwardly-directed, horizontal lip. The upper end of the stake is adapted to abut against the base portion of the upper section of the forming strip. Also, the upper end of the stake includes a protrusion in the form of a tab-like segment which extends outwardly and downwardly from the support stake, whereby this protrusion will snap into engagement with the horizontal lip of the downturned flange so that the forming strip will be retained on the stake. However, this construction envisions that the upper edge of the stake will abut against the base portion of the upper section of the forming strip, and moreover the horizontal lip will engage beneath the lanced protrusion, so that there is no vertical adjustability available in this design. This patent shows a precision design which requires ideal working conditions, close tolerances, and which lacks vertical adjustability and provides a weak locking action between the form and its supporting stakes.
The Heltzel U.S. Pat. No. 1,345,179 describes a portable concrete form with adjustable means for use with concrete structures requiring various heights. A concrete mold form is supported on a pluraltiy of stakes, where each stake is provided with a flange for restricting movement of the stake into the ground. Each stake is provided with a plurality of vertically-arranged notches for supporting a bracket member at various elevations. The concrete form is hung from this bracket member on each stake. In all cases, the stakes of this Heltzel patent protrude above the top edge of the concrete forms so that a screed could not be used, as in the present invention, to move across the top edge of the concrete form that serves as as leveling guide so as to smooth out the concrete surface.